The iontophoresis for permeating, into the living body, an ionic medicine useful for the living body by utilizing the electrophoresis has also been called ionic permeation therapy or ion introduction method, and has been widely known as a method of administering a medicine of a required amount into a diseased part in a pain-free state.
In the iontophoresis, so far, a medicine-containing layer impregnated with an ionic medicine is placed on the living body, a working electrode is arranged on the side opposite to the living body with the medicine layer sandwiched therebetween, a counter electrode is placed on the living body separated away from the medicine-containing layer, and an electric current is permitted to flow across the working electrode and the counter electrode from a power source causing the ionic medicine to permeate into the living body. This method has an object of permeating the ionic medicine only into the living body through the living body interface such as the skin and the mucous membrane. According to this method, however, the ionic medicine does not necessarily pass through the living body interface but, conversely, it often happens that sodium cations, potassium cations and chloride anions permeate back into the medicine layer from the side of the living body. In particular, ionic medicines that are believed to be useful for the living body have a smaller mobility than those of ions existing in the living body, and a desired medicine is not efficiently administered (does not efficiently permeate into the living body) in proportion to the time the electricity is supplied. In the iontophoresis, further, the medicine comes into direct contact with the electrodes triggering a reaction on the electrodes not only wasting the medicine but also forming compounds that may adversely affect the living body. Moreover, the medicine is usually used in the form of an aqueous solution. Therefore, the electrolysis of water takes place on the working electrode and on the counter electrode, whereby the pH of the medicine-containing aqueous solution varies due to H+ ions and OH− ions that are formed often causing the living body to be inflamed.
In order to solve these problems, new iontophoretic methods have been proposed by arranging an ion-exchange membrane on the living body interface so that ionic medicine permeates into the living body through the ion-exchange membrane (e.g., see patent documents 1 to 4).
[Patent document 1] JP-A-3-94771
[Patent document 2] JP-T-3-504343
[Patent document 3] JP-A-4-297277
[Patent document 4] JP-A-2000-229128
According to the systems proposed in the above patent documents, the ion-exchange membrane arranged on the living body interface permits the permeation of only those ions having the same charge as the desired medicine ions. This makes it possible to prevent the ions having a charge opposite to that of the desired medicine from oozing out of the living body and, hence, to accomplish a high dosage of the medicine as compared with when no ion-exchange membrane is arranged. The above technologies use a commercial ion-exchange membrane which employs, as a reinforcing member (reinforcement), a woven fabric, that is used for the manufacture of the salt and for the dialysis of food compounds.
So far, the iontophoresis has used a large device and could be practiced in particular places only such as in a hospital. In order to realize the iontophoresis at any time in any place, therefore, study has been forwarded vigorously concerning the iontophoresis devices that feature simple and compact structures and that can be carried.
The iontophoresis device of the portable type usually uses cells such as button-type cells as a power source. Therefore, the dosage of the medicine becomes particularly important when the voltage remains constant (constant voltage) rather than when the current remains constant (constant current).
Further, the administration of medicine by the iontophoresis and, particularly, the administration of medicine by using a portable iontophoresis device is continued over a relatively long period of time unlike that of the method such as the injection. It is therefore desired that the patient is allowed to move around and behave while carrying the iontophoresis device.
However, even the above iontophoresis method using the ion-exchange membrane is not satisfactory concerning the dosage of the medicine and, particularly, the dosage of the medicine in a constant-voltage state, and it has been desired to accomplish a further improved dosage.
Further, if the patient behaves while carrying the iontophoresis device, the portions of the skin to where the iontophoresis device is fitted are expanded, contracted and bent. Therefore, the ion-exchange membrane used for the iontophoresis device must be so strong as will not be broken by the stress generated by the expansion, contraction and bending. In general, the membrane exhibits a strength that increases with an increase in the thickness thereof. However, an increase in the thickness of the membrane, at the same time, causes a decrease in the flexibility and, hence, a decrease in the follow-up property for the expansion, contraction and bending. Therefore, if an ion-exchange membrane having a large thickness is used by giving importance to the strength, then, such problems arouse that the iontophoresis device peels off the skin or is disconnected while being carried.